1. Field of the Invention
The present invention generally relates to a touch sensor, and in particular, to a capacitive touch sensor.
2. Description of the Related Art
A touch sensor has been widely used as an input device for electronic appliances, portable communication terminals, or industrial installation equipment. The touch sensor allows selection of various input patterns, such as handwriting and simplification of an external structure. A user's sense of pressing in the touch sensor is degraded when compared to a dome-switch type input device.
Moreover, the input devices of a touch sensor type have to include means for allowing users to make accurate selections in poor environments, such as a backlighting means. The backlighting means of the touch sensor improves user's visibility when the touch sensor is used in a dark environment, thereby allowing the user to check if a desired button is pressed. A plurality of light emitting diodes may be surface-mounted on a circuit board in the backlighting means, and light from the light emitting diodes may be emitted directly to the touch sensor.
FIG. 1 illustrates the structure of a conventional touch sensor 100. Referring to FIG. 1, the touch sensor 100 includes a touch panel 110 having an electrode layer 111 and a Printed Circuit Board (PCB) 120 disposed below the touch panel 110. The touch panel 110 includes a substrate 112 capable of transmitting light in a visible wavelength band and the electrode layer 111 disposed on the substrate 112. The substrate 112 may be made of a dielectric material except for a metal material. The electrode layer 111 may have at least one electrode patterns 111a and 111b formed on its top face in order to form electrical contacts by user's touch.
The PCB 120 includes circuits for controlling and driving the touch sensor 100 and at least one light source 121 and 122 for backlighting the touch panel 110. The light sources 121 and 122 may be light emitting diodes and may be surface-mounted on the top face of the PCB 120. The light sources 121 and 122 are surrounded by guide means 131 and 132 for guiding generated light towards the substrate 112.
However, the conventional touch sensor 100 has to include the light sources 121 and 122 for backlighting and the guide means 131 and 132, and the light sources 121 and 122, the electrode patterns 111a and 111b, and the guide means 131 and 132 have to be arranged in the vertical direction. That is, in the conventional touch sensor 100, the electrode patterns 111a and 111b and the light sources 121 and 122 have to be in one-to-one correspondence, thus increasing volume, power consumption, and manufacturing cost.
Moreover, since the space for minimizing the influence of an electromagnetic wave in the touch sensor 100 increases the thickness of the touch sensor 100, the touch sensor 100 is not suitable for use in small-size portable image devices.